1. Field of the Invention
The invention relates to a method for depositing a polymer layer containing nano-material on a substrate material, comprising the steps of providing the substrate material and providing a polymerization material near a surface of the substrate material.
By attaching nanoparticles or depositing a polymer layer containing nanoparticles on a substrate material, such as textile, surface features of the material can be significantly changed, e.g. the performance of textile in terms of stain-resistance improves, without affecting bulk properties of the material. There are several methods already available and used to apply nanoparticles onto a surface of a substrate material. Those methods may be divided basically into wet techniques and dry techniques.
2. Prior Art
A typical representative of wet techniques is a sol-gel technique. It is a versatile solution process that is suitable to make nanocoatings and polymer matrix composites with nanoparticles. The starting materials used in the preparation of the ‘sol’ are usually inorganic metal salts or metal organic compounds such as metal alkoxides. To create solid ‘gel’ on a surface, coating methods such as dip and spin coatings are used. Preparation of hybrid materials that incorporate inorganic systems, such as nanoparticles, into an organic polymeric matrix by sol-gel, or by the incorporation of metals and metal complexes in polymers by coordination interactions, is reviewed by G. Kickelbick (Prog. Polym. Sci. 28, 2003, pp. 83-114). Disadvantages of the techniques, besides those associated with wet processing, are that they require complicated procedures and multi-step processing and a limited sort of nanoparticles may be deposited by these techniques.
A self-assembled nanolayer (SAN) technique has been used to incorporate nanoparticles onto charged textile fibers. The technique is based on the effect of electrostatic attraction between a charged substrate fibre and oppositely charged nanoparticles contained in a solution. The deposition process may be well controlled but a multi-step processing is required and a limited sort of nanoparticles may be deposited by this technique.
Other prior art belonging to the group of wet methods is disclosed in patent publications WO 01 06054 A1 and U.S. Pat. No. 6,607,994 B2, which describe how to durably attach nanoparticles to fibers, yarns, fabrics, and/or textiles (webs) and thus impose various and substantially permanent properties to those materials. The term “nanoparticle” is considered rather generally in those two patents, and it covers an agent or a payload surrounded by or contained within a polymeric encapsulator, which includes functional groups for binding or attachment of the nanoparticle to the treated material. The nanoparticle may also comprise a polymeric shell surrounding the agent/payload and a three-dimensional polymeric network entrapping the agent/payload or a reactive surface coating. Alternatively, the surface of the nanoparticle includes functional groups that can bind to a linker molecule, which will in turn bind or attach the nanoparticle to the treated material. The nature and formulation of the polymeric encapsulator allows a controlled release, from zero to prolonged and constant, of the entrapped payload. Various wet processes such as soaking, spraying, dipping, fluid-flow, padding and the like are used to permanently attach nanoparticles to the treated material by its exposure to a solution or dispersion/emulsion of the textile-reactive nanoparticles, optionally also to a catalyst and/or a linker compound, and subsequent drying.
Patent publication U.S. Pat. No. 6,723,378 B2 discloses a way how to achieve water repellency, fire-retardancy and/or thermal insulation of fibers and fabrics produced from fibers by filling void spaces in the fibers and/or fabrics with a finely divided powdered material, including nanopowder with particles in the size range of 1-500 nm. Sufficiently finely divided powder attach to the fabric's fibers and resist the tendency to be removed from the fabric. Void spaces are filled in by powdered material by filling the voids with a solution that precipitates particles as it dries, by filling the voids with a solution containing a colloidal suspension of particles that remains when the liquid dries, by passing the powder over fibers or forcing the powder to enter the space using various methods. The main disadvantage of this approach for example for the treatment of military clothing or for the protective clothing against chemical and biological agents is that only limited amount of nanoparticles may be attached to the fibers. Further, only very small particles will durably attach to the fibers.
An example of another work based on a wet technique is disclosed in two patent publications, viz. U.S. Pat. No. 6,645,569 B2 and U.S. Pat. No. 6,863,933 B2. In patent publication U.S. Pat. No. 6,645,569 B2 is described a method of applying nanoparticles to a surface, preferably to a soft surface by inject printing and, generally, by any suitable printing technology. Other wet ways of applying nanoparticles to a surface are also mentioned, such as spraying and a dipping and/or soaking process, and such as applying a coating composition containing nanoparticles during a washing or rinsing processes. Plasma treatment is mentioned in claim 7 of the publication but just as one of methods that can be used for a surface energy treatment before using a wet technique for the application of nanoparticles to the said surface. The purpose of the surface energy treatment, e.g. plasma treatment, is “to enhance the ability of the surface to receive the coating composition” containg nanoparticles. In patent publication U.S. Pat. No. 6,863,933 B2 is described a method of hydrophylizing materials, but also of producing other surface modifications of all types of soft surfaces and in some cases hard surfaces, by applying a coating composition containing nanoparticles. Wet techniques how to apply nanoparticles to a surface are those already described in U.S. Pat. No. 6,645,569 B2. Plasma treatment and other treatments are mentioned in claim 6 of the publication in connection with the step of increasing the surface energy of a material but again only before the application of nanoparticles to the said surface by some of the listed wet techniques.
Patent publication U.S. Pat. No. 6,838,816 B2 discloses another example of using a traditional wet coating method such as spray, dip coating or spin coating for the deposition of nanoparticles. In this patent, monodispersed colloid light-emitting nanoparticles of oxides, semiconductors and polymers are deposited on a substrate to fabricate a light emitting diode (LED).
Patent publication U.S. Pat. No. 6,723,388 B2 describes the deposition of nanostructured films comprising one or more metals or metal oxides, optionally with embedded nanopores. By nanostructured film is meant a thin film with a nanoscale domain structure or with nanoparticles in the structure. Nanoporous film refers to a thin film with pores having diameters in the nanometer range. The films are deposited in two steps. In the first step, a precursor solution film is applied on a substrate surface by traditional techniques such as spin coating, spraying, dip coating or inking. In the second step, the film is converted into a nanostructured and/or nanoporous film by a low temperature chemical reaction in a suitable atmosphere. The conversion is initiated for example by light of a suitable wavelength, a plasma and electron or ion beams. This approach can be used for various applications for example for which the nanostructure and a high surface area are important, such as the deposition of sensor or catalyst materials or for the deposition of patterned films in microelectronics industry. Main weaknesses of the approach, besides those associated with wet processing, are that the choice of building nanomaterial is limited and the method, as it is disclosed in the patent publication, is focused on the deposition of films comprising one or more metals or metal oxides from precursor formulations containing metal-organic compounds.
Main drawbacks of wet processing, and in particular in textile wet processing industry, are environmental problems due to the use of a whole host of harmful chemicals, vast amounts of water needed and polluted, and high energy costs due to heating, drying and curing processes. Further, the deposition a homogeneous dispersion of nanoparticles is often difficult and the choice in the type of nanoparticles that can be attached to a substrate is limited. Some wet deposition processes are diffucult to scale-up due to the complicated multi-step processing in which some steps, like spin-coating, are not suitable for the on-line treatment.
Main dry deposition techniques of nanostructured thin films and thin films comprising nanoparticles include physical vapour deposition (PVD) or sputtering, chemical vapour deposition (CVD), and a group of so-called impaction techniques.
PVD is a thin film deposition process in the gas phase in which a source material is physically transferred in the vacuum to a substrate without any chemical reactions involved. PVD includes the step of evaporation or sputtering of the source material to be deposited. Sputtering results from the bombardment of a solid target by high energy chemically inert ions extracted from plasma, the bombardment causing ejection of atoms from the target. The vapour then condensates in the case of evaporation, or the ejected atoms are then re-deposited in the case of sputtering on the surface of a substrate to form a thin film. PVD is commonly used to deposit metals. A metal sputtering process or a metal evaporation process in combination with a low pressure plasma polymerization has been used to deposit a polymer layer containing metal nanoparticles (A. Heilmann, Polymer Films with Embedded Metal Nanoparticles, Springer-Verlag Berlin Heidelberg 2003, ISBN 3-540-43151-9). Problem of this approach for many practical applications, e.g. for applications in the textile industry processing, is that both the metal sputtering process and the metal evaporation process require a high vacuum operation and is essentially limited to metal type nanoparticles in the polymer layer.
There are two main types of CVD processes: thermal CVD and plasma enhanced CVD (PECVD). Deposited species are formed as a result of chemical reactions taking place at elevated temperatures in thermal CVD. Gaseous reactants chemically react in the vicinity of a substrate and a solid product of the reactions is deposited on the substrate surface. In PECVD, a non-thermal plasma is used to generate the desired chemical reactions. As a result, deposition using the same source gases is taking place at lower substrate temperature in PECVD then in thermal CVD.
Patent publication WO 03 066933 A1 discloses a method for depositing hybrid organic-inorganic coatings to a substrate by the use of PECVD at reduced pressure. According to the patent publication, the inorganic component may also comprise nanoparticles, which are homogeneously distributed in the deposited organic component. Both organic and inorganic components, including nanoparticles, are formed through the dissociation of precursors in plasma. A limitation of the disclosed method is that only inorganic nanoparticles may be deposited in an organic component. Further, as nanoparticles are created in the plasma process, characteristics of the deposited hybrid coating, such as size and size distribution of nanoparticles, their surface density, uniformity and homogeneity are not easy to control. Last but not least, the disclosed system operates at reduced pressure and is suitable for the treatment of relatively small substrates and batch processing. It is not fitted for a continuous line operation, which is the must for many processing such as in the textile industry.
Impaction techniques allow depositing fine-grained deposits and coatings with a nanoscale domain structure but they are not convenient for depositing individual nanoparticles. Impaction techniques include for example hypersonic plasma particle deposition (HPPD), gas jet deposition (GJD) and focused particle beam deposition (FPBD). A thermal spray process may also be included in the category of impaction techniques. The impaction techniques are based on the deposition and attachment of nanoparticles to form nanostructured coatings by impaction. It means that nanoparticles are attached to a substrate by their acceleration and high-speed impaction on the substrate surface.
FPBD is described and overview of literature related to other impaction techniques is summarized in patent publication WO 02 05969 A3. Nanoparticles in FPBD are generated in gas phase for example in a DC torch, a thermal plasma reactor, an evaporation-condensation reactor or by laser pyrolysis. They are accelerated in a low pressure (below 10 torr) expansion chamber, collimated by a system of focusing elements and deposited by the impaction on a substrate that is placed in an evacuated deposition chamber with pressure in the order of 0.01 torr and below.
Impaction-based techniques are in general suitable for the deposition on hard surfaces and not on soft and heat sensitive materials such as for example textile. Further, the approach is not convenient for applications that require deposits of individual nanoparticles with well-controlled size, size distribution, surface density and uniformity. The approach is not suitable for the deposition of nanoparticles on inner surfaces of a structured material, e.g. on individual fibers of a textile material, and only a limited sort of nanoparticles may be deposited.
A thermal spray process uses a device to molten or heat-softened a coating material, which is then accelerated and propelled at a high velocity towards a substrate. The hot material impacts on the substrate surface and rapidly cools forming a coating there. Patent publications U.S. 2001 0004473 A1, U.S. Pat. No. 6,277,448 B2 and EP 1 134 302 A1 describe the deposition of a high quality nanostructured coating when the source of coating material is a nanoparticle powder delivered from outside or nanoparticles formed from a precursor directly in the thermal spray device. Patent publication WO 02 102903 A2 discloses synthesis and deposition of luminescent films from a liquid precursor mixture also utilizing a plasma spraying deposition technique. The deposits are composed of randomly oriented nano- to micron-sized grains.
Patent publication U.S. Pat. No. 6,235,351 B1 discloses the application of a coating of nanoparticles on surfaces such as “building exteriors, ship decks and exposed hull portions, aircraft wings and fuselages”. The purpose of coating is to create a self-decontaminating surface against chemical and biological contaminants. The coating is achieved by a thermal spray surface deposition in which nanoparticles in an alcohol suspension are fed into a plasma spray gun and are heated there to a temperature of at least 750° C. and are projected on a treated surface on which they splatter and solidify.
Similar to previously mentioned impaction techniques, thermal spray process is not applicable for the deposits of individual nanoparticles in uniform and homogeneous way and for the treatment of soft and heat sensitive surfaces and materials such as textile. Also, the choice of nanoparticles that may be applied is limited due to the high processing temperature.
In the U.S. Pat. No. 6,616,987 is disclosed a process for manipulating particles in a plasma in order to achieve their non-uniform spatial distribution in the plasma and for arranging and adhering at least a portion of those particles on a substrate. However, the process requires low pressure operation and is focused on achieving a non-uniform distribution of nanocrystalline semiconductor particles both in plasma and in the coating, which is a semiconductor layer.